Nonwoven web laminates have application in a variety of disposable products, including wipers, garments, medical drapes and absorbent articles such as diapers. One class of such nonwoven web laminates is commonly referred to as spunbonded/meltblown/spunbonded (SMS) laminates. These SMS laminates generally consist of nonwoven outer layers of spunbonded polyolefins and an interior layer of meltblown polyolefins.
As used herein, the term "nonwoven web" refers to a web that has a structure of individual fibers or filaments which are interlaid, but not in an identifiable repeating pattern.
As used herein, the term "spunbonded fibers" refers to fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinnerette. Cooling air is fed to a quenching chamber wherein the filaments are cooled. The cooling air is then sucked through a nozzle, which accelerates the flow of air. The friction between the flowing air and the filaments creates a force which draws the filaments, i.e., attenuates the filaments to a smaller diameter. The drawn filaments are then passed through a diffusor and deposited on a conveyor belt to form a nonwoven web. A conventional spinbonding technique is disclosed in U.S. Pat. No. 4,340,563 to Appel.
As used herein, the term "meltblown fibers" refers to fibers which are formed by extruding molten thermoplastic material as threads or filaments through a plurality of fine, usually circular capillaries of a die. A high-velocity, usually heated gas (e.g., air) stream attenuates the filaments of molten thermoplastic material to reduce their diameter. Thereafter the meltblown fibers are carried by the high-velocity heated gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. A conventional meltblowing technique is disclosed in U.S. Pat. No. 4,707,398 to Boggs.
Meltblown fibers differ from spunbonded fibers in that the extruded polymer strands have much finer diameters. These fine diameter filaments are easily dispersed by the forced hot air stream before being deposited on the collecting surface. In addition, the meltblown fibers are substantially cooled by the air so that they do not significantly bond together. Bonding of the web to retain integrity and strength occurs as a separate downstream operation.
SMS laminates have found numerous applications. U.S. Pat. No. 4,374,888 to Bornslaeger discloses an SMS fabric suitable for use as a recreational fabric in the manufacture of tents, outer garments, tarpaulins and the like.
U.S. Pat. No. 4,766,029 to Brock discloses a house wrap consisting of an SMS laminate. The external layers are spunbonded polypropylene. The interior layer is a two-component meltblown layer of polyethylene and polypropylene. The laminate is calendared after formation so that the polyethylene melts and flows to close up the interstitial space and to bond the layers together to create a strong semi-permeable laminate.
U.S. Pat. No. 4,863,785 to Berman discloses a nonwoven composite material comprising a meltblown fabric layer of a thermoplastic polymer sandwiched between two prebonded, spunbonded reinforcing fabric layers of a thermoplastic polymer. The preferred thermoplastic polymer for both the meltblown and spunbonded layers is polypropylene.
U.S. Pat. Nos. 5,145,727 and 5,149,576 to Potts disclose a composite nonwoven including melt-extruded layers (defined as including spunbond and meltblown webs) in which fibers between the layers intermingle to form a phase boundary. The fibers of at least one of the layers is prepared by melt extrusion of a mixture of an additive and thermoplastic polymer through a die. The additive preferentially migrates to the surface of the fibers, thus imparting a selected surface characteristic to a single layer in the composite, but does not migrate to the adjoining layer. Preferred additives may impart, for example, hydrophilicity or hydrophobicity to the layer.
U.S. Pat. No. 3,730,184 to Mesek discloses a disposable diaper having a topsheet made of bonded nonwoven fabric. The mid-portion of the bonded fabric is treated with a surfactant to minimize the water repellent effect of the binder and to make the mid-portion of the fabric readily wettable. The web is impregnated with a binder fluid by flowing a solution or dispersion of the binder over the web. The central portion of the facing web is also treated with a surfactant added to the binder fluid. The binder fluid is fed to a weir box having an opening which allows the binder fluid with surfactant to pour over the central region of the web.
U.S. Pat. No. 4,112,153 to Butterworth discloses a method for controlling the water repellency in a predetermined region or zone of a nonwoven fabric. The method comprises bonding the fabric using a binder solution or suspension containing a surfactant that can be denatured or even degraded at elevated temperatures. The fabric is then subjected to a heat treatment so that in predetermined areas or regions of the fabric the surfactant that is present is denatured to provide the desired degree of hydrophobicity.
U.S. Pat. No. 4,328,279 to Meitner discloses a clean room wiper treated with surfactant. The Meitner '279 patent discloses that the surfactant can be applied by spraying, dipping, coating, impregnating or printing.
U.S. Pat. No. 4,585,449 to Karami discloses a disposable diaper having a spunbonded topsheet containing surfactant. The surfactant is applied by spraying, printing or roller coating the entire surface or in limited areas such as the central portion. Alternatively, the surfactant is line or spot printed on the topsheet to improve fluid penetration.
U.S. Pat. No. 4,950,264 to Osborn discloses a sanitary napkin having a topsheet rendered hydrophilic by treatment with surfactant. The surfactant is applied by spraying, padding or the use of transfer rolls.
U.S. Pat. No. 4,861,652 to Lippert discloses that diaper topsheets are typically composed of a liquid-permeable, substantially hydrophobic material such as a spunbonded web composed of synthetic polymer filaments. Alternatively, the topsheet may comprise a melt-blown web or a bonded carded web composed of synthetic polymer filaments. Suitable synthetic polymers include, for example, polyethylene, polypropylene and polyesters. The topsheet must have a pore size that readily allows the passage therethrough of liquids, such as urine and other body exudates. The Lippert '652 patent also discloses that the topsheet can optionally be treated with surfactants to selectively adjust its degree of wettability.
U.S. Pat. No. 5,562,650 to Everett discloses that a diaper topsheet can be surface treated with surfactant by any conventional means, such as spraying, printing and brush coating. The surfactant material can be applied to a medial section of the topsheet layer to provide a greater wettability of the medial section, as compared to a remainder of the topsheet layer.
U.S. Pat. No. 5,330,456 to Robinson discloses a disposable absorbent panel assembly having a topsheet made of carded, spunlaced, spunbonded or thermally bonded polypropylene or polyester nonwoven fabric. The lateral central portion of the topsheet is rendered hydrophilic by application of surfactant.
U.S. Pat. No. 5,486,381 to Cleveland discloses a continuous process for non-compressively and uniformly applying a liquid saturant, such as surfactant, throughout a permeable sheet. A laminar flowing curtain of liquid saturant is deposited on one side of the permeable sheet and a vacuum is applied to the other side to generate a substantially uniform distribution of saturant throughout the sheet.
In accordance with prior practice in the manufacture of disposable diapers, separate components are used for the hydrophilic and hydrophobic regions. For example, an absorbent article consists of a topsheet which is hydrophilic and a cuff which is hydrophobic and is attached to the topsheet. The topsheet helps in fluid transfer to the absorbent core, while the cuff prevents leakage. It is known to use spunbonded fabric in the hydrophilic regions.